assert(«CONDITION»)
- Check that CONDITION is true.
- If not, stop (crash gracefully) and report error immediately.
- CONDITION must be true if *your code* is correct.
  - Do not use this for checking if someone else's code called your code correctly.
  - Do not use this to check a file exists.
  - Do not use this to check if the system is working properly and in a good state.
- assert(…) lets you write code that tests itself.
- assert(…) documents what you believe to be true in a dependable way.
  - Try to write the CONDITION to be clear and understandable.
- Use this with sanity checks.
- Not a substitute for regular testing.
  - Occassionally, I may use assert(…) for testing learning examples.
- If CONDITION is false, then you know that *your code* has a *bug*.
  - "bug" means the programmer made a mistake.
  - "error" means something unexpected happened that interrupted the desired behavior.
    - ex: file not found
    - ex: someone else called our code incorrectly